Electrodynamic transmitter



July 14, 1936. c. A. HARTMANN y 2,047,777

ELECTRODYNAMIC TRANSMITTER V Filed Aug. 2o, 19:51v

Patented July 1.4, 1936 I i l UNITED STATES PATENT OFFICE ELECTRODYNAMIC TRANSMITTER Carl' Albert Hartmann, Berln-Siemensstadt,

Germany, assgnor to Siemens & Halske, Aktiengesellschaft, Siemensstadt, near `Berlin, Germany, a corporation of Germany Application August 20, 1931, Serial No. 558,314

In Germany August 21, 1930 9 Claims. (Cl. 179-121) Thelnvention' relates to electro-dynamic translonance frequency are no longer acted on appremitters having diaphragms traversed by current, ciably by the end conditions, provided the transand is more particularly concerned with ribbon verse resonance frequency is sufficiently high. transmitters. The reduction of the chamber behind the rib- In the constructional design of ribbon transbon would considerably reduce the ribbon ampli- 5 mitters, the en tire chamber behind the ribbon tude outside the resonance range, owing to the up to the immediate neighbourhood thereof is stiffness of the air-cushion. According to the inlled with a felt packing. The operation of such vention, the remainder of the previous large a device is as follows: At low frequencies, only chamber at the back, and embraced by 'the mag- 10 the resonance of the ribbon whose peak lies at net-legs, is therefore coupled to the chamber be- 10 about 100-200 cycles is noticeable; in the range hind the ribbon, with the result that its resof intermediate frequencies, the resonance of the onance is again set up in the intermediate frechamber coupled to the ribbon is also manifest. quency range. In order to obtain the transverse As to its situation and selectivity, it depends on resonance nevertheless in the small chamber, the i3 the felt packing and, furthermore, on the way `in coupling is, for instance, effected through a slot. 15 which the chamber is connected to the outer air. This slot is so dimensioned that, already some- The ribbon transmitters developed in this manwhat below the resonance frequency of the small ner meet, in general; all the requirements inchamber, its damping is sufficiently high to pre'- volved in satisfactory transmission. However, vent appreciable sound energies from entering the no they have the disadvantages of low sensitivity for large chamber. At high frequencies, the air rehigh frequencies, and of causing noticeable varimains, so to speak, within the slot. This pracations in 'the reproduction of the intermediate tically means an automatic coupling of the large frequencies in the case of different transmitters, chamber at high frequencies. F01' the range 0f the latter being due to the variationsin the felt intermediate frequencies. h0WeV1,-the TES- packings of such transmitters. It is, therefore, Onane range 0f the large ChambeL-the SlOt 25 difficult to produce in quantities .transmitters damping must be negligibly low.

having similar characteristics. However, quan- Instead of the slot, provision may also be made tity production is desirable for technical purfor narrow holes or the like, which present the poses and for reasons of economy, resistance required for high frequencies. so According to the invention, these drawbacks The drawings show a constructional example can beavoided and the reproduction of frequenof the object 0f the irlVeIltOrl.

cies, particularly the high frequencies,I can be Fig. 1 shows a cross-sectional view of the transimproved by placing one or several resonators mitter; Fig. 2 a section in the direction A-B of behind the ribbon. Use should preferably be Fig. 1. Fig. 3 is a performance curve ofthe 'E made of a well-defined chamber behind the ribtransmitter.

`bon as a resonator. Together with the ribbon In the air-gap 0f the magnet 1, there is armass, it is designed to provide .for a natural os. Ranged a IbbOn 2 and behind it the chamber or cillation (transverse resonance) in the high freresonator I, which is in connection with the quency range, for instance at 400 cycles. chamber or resonator 3 throughthe slot 4. The 40 `By means of this resonance the reproduction large Chamber 3 iS Packed With felt in a well- 40 of high frequencies is materially improved, known manner; the resonator l is connected whereas without this chamber, the frequencyV with the outer air through gauze-covered apercharacteristics would slope down considerably. turcs 6. Wider slots 5 connect also the resonator A further improvementfor the highest frequen- 3 with the outside air. h cies-is obtained by means of the longitudinal The various resonance frequencies must be 4 resonancelsinging effect) of the chamber. The chosen so as to avoid spaces in the frequency natural-oscillation of the longitudinal resonance v characteristics. This condition is fulfilled if the is caused to lie at about 8000 cycles. It isthe various resonators are `strongly damped. The fundamental frequency of the chamber behind damping is obtained for-the large chamber 3 by 50 the ribbon which is open at both ends (top and means .of a felt packing applied in a weil-known bottomh The fact that the chamber is open at manner. In addition, the damping is increased its ends does not impair the production of transby the apertures 5 through which the chamber 3 verse resonance, since the pressure conditions beis connected with the outside air. The same holds 5 hind the ribbon centre at the transverse restrue for the small chamber l which is kept in 55 touch with the outside air by means of the gauze windows 6. The energy delivered to the coupling slot l further increases the damping of the small chamber I.

The performance of the new ribbon transmitter, with respect to the different frequencies of the incident sound, will be explained with reference to Fig. 3. For the lowest frequencies, it is the natural oscillation of the ribbon (curve I) which is decisive. It is very soon superimposed for intermediate frequencies by the resonance frequency of the large chamber (curve 2). In proportionas the frequency is further increased, the slot effect of the large chamber is stopped, the transverse resonance of the small chamber (curve 3) becomes effective and prevents a reduction in sensitivity (curve 4).

The new structure provides a wider frequency band and the possibility of manufacturing uniform apparatus. Even though in the range of intermediate frequencies the influence of the felt packing is noticeable, the well-defined resonator l in the immediate neighbourhood of the ribbon and its disconnection by means of the slot avoids the action of the felt at the higherfrequencies. The frequency characteristic of the transmitter varies if it is used in another atmosphere, say within a hydrogen-atmosphere, which may sometimes be recommendable. The transverse resonance does not vary if another medium is chosen, Whereas the longitudinal resonance, as a function of the sound velocity in the medium involved, is subject to considerable variations.

I claim.

1. In a transmitter of the class described, a magnet, a conductive ribbon disposed between the poles of said magnet and adapted to carry alternating currents of frequencies Within the audible range, said ribbon having a natural frequency of about 30 to 200 cycles, a high frequency resonator disposed adjacent said` ribbon, said resonator having two resonance frequencies, one of them being about 4000 cycles and the other about 8000 cycles, an intermediate frequency resonator disposed in series connection with said high frequency resonator, the natural frequency of said intermediate frequency resonator being about 300 to 800 cycles, passages for making said series connection, said passages preventing the passing of high frequencies, apertures connecting with the exterior for damping said high frequency resonator and sound irnpeding means for damping said intermediate frequency resonator.

2. An electro-dynamic transmitter comprising, a magnet, a conductive ribbon disposed between the poles of said magnet and adapted to carry alternating current frequencies within the audible range, the natural frequency of said ribbon being less than 200 cycles, means forming a high frequency resonator adjacent said ribbon, means forming an intermediate frequency resonator adjacent said high frequency resonator, passages in said first means for connecting said resonators in series, said passages being impervious to high frequencies apertures for damping said high frequency resonator, and sound impeding 'means for damping said intermediate frequency resonacent said ribbon, an intermediate frequency resonator disposed adjacent said high frequency resonator, the natural frequencies of said resonators differing by more than one octave, passages in said means impervious to high frequencies for connecting said resonators in series, apertures in said means opening to the exterior for damping said high frequency resonator, and sound impeding means for damping said intermediate frequency resonator.

4. In an electro-dynamic transmitter having a yieldable conductive ribbon and a plurality of relatively highly damped serially connected resonators, an air chamber in back of said ribbon toward and from which said ribbon can freely oscillate, the natural frequency of said air chamber being within the range of high frequencies, ,and an aperture in the wall of said air chamber for damping the same.

5. An electro-dynamic transmitter of the class described comprising, a yieldable conductive ribbon, an air chamber -in back of said ribbon tof ward and from which said ribbon can freely oscillate, said air chamber forming alresonator the natural frequency of which is within the range of high frequencies, and an opening in the wall of said air chamber so dimensioned as to impede the passage of high frequencies therethrough.

7. In a transmitter of the class described'arranged to cover a large range of frequencies and including a plurality of vibratory structures each of a different natural frequency coupled with one another in series relation, a yieldable conductive ribbon, an'auxiliary resonator in back of said ribbon comprising means forming an air chamber toward and from which said ribbon can freely oscillate, the natural frequency of said air chamber being-in the range of high frequencies, and an opening in said means which is impervious to high frequencies for establishing series relation with anotherv vibratory structure.

8. An electro-dynamic transmitter comprising, a conductive ribbon disposed between the poles of a magnet, the natural frequency of said ribbon being within the low frequency range, an air chamber in back of said ribbon, the natural frequency of said chamber being in the range of high frequencies, an opening in the wall forming said chamber, said opening being impervious to high frequencies, and additional resonance chamber means arranged in series relation behind said ribbon and said first chamber, said last named means being tuned to a natural frequency different from the others.

9. An electro dynamic transmitter comprising a conductive ribbon disposed between the poles of a magnet, a plurality of relatively highly damped vibratory structures each tuned to a natural frequency different from the other disposed in back of said ribbon and serially related thereto, coupling means intermediate of said structures arranged to maintain said series relation therebetween, said coupling means comprislng a member having an aperture which is substantially impervious to high frequencies.

CARL ALBERT HARTMANN. 

